In digital oscilloscopes, there are two instances in which it is desirable to shift the level of a signal. One is in the input signal preamplifier stage to position the signal within the operating-limit window of an analog-to-digital converter (ADC), and the other is in the display-generating circuits to provide vertical positioning of the display. Since both of these functions entail basically the same operation, i.e., adding or subtracting voltage, it is desirable to utilize a single position control to perform both functions. However, a problem arises in that the display screen vertical center corresponds to the center of the ADC window, so that if voltage is added to the input signal to shift it within the ADC window in the waveform acquisition mode, that voltage is also added to the display signal in the display mode, causing the display signal to shift off-screen.